This patch exposes DMA addresses in URBs.  It exposes new APIs that
let drivers be a bit smarter in terms of DMA, reducing USB overhead
on some platforms (but not commodity pcs).  As discussed with DaveM,
and on the usb-devel list.

Supporting patches are still needed.  Of course, there's teaching HCDs
to use _these_ addresses when they're provided (easy).  There's also
teaching drivers (like hid) to use the new usb_buffer_alloc() support,;
can happen incrementally.  And adding scatterlist support, which will
be desirable for usb-storage and hpusbscanner.  But this is the start
needed to get all of that going.